A conventional label printer has torsion springs (or friction members such as pieces of wool felt) arranged at its ribbon supply shaft and ribbon take-up shaft, so as to maintain ribbon tension during a printing process, and rewind a carbon ribbon for a short distance through the elastic force of the torsion springs after a printed label is torn off. In this way, before the printer prints the next label, a portion that is left protruding out of the printer after the previous printing process can be rewound to facilitate a subsequent printing process.
However, the conventional torsion-spring-aided ribbon rewinding design for a label printer only allows the carbon ribbon to be rewound for a short distance. In applications requiring printing of longer distances, the carbon ribbon cannot be rewound completely. As a solution, driving the ribbon supply shaft and the ribbon take-up shaft respectively by a direct current (DC) motor to rewind the carbon ribbon has been proposed. However, such a solution not only involves a more complicated overall mechanism and incurs higher costs, but is prone to cause the carbon ribbon to be too loose or too tight if there is an improper rotational speed design or a change in motor characteristics after being used for a long time.
A loose carbon ribbon may cause ribbon wrinkling during a printing process, and therefore affect printing quality; and a carbon ribbon that is too tight is prone to break.
As the technical solution of driving the ribbon supply shaft and the ribbon take-up shaft respectively by a DC motor to rewind a belt body not only incurs higher costs and difficulties in adjusting for ideal working conditions, but also has less-than-desired stability, there is still room for improvement in belt body rewinding techniques.